The present invention is directed to a novel control valve utilizing the well-known split-disc check valve design disclosed in U.S. Pat. Nos. 3,072,141, 3,965,926, and 4,005,732. The split-disc check valve, or dual-plate check valve, is a type of check valve that incorporates two separately-pivotal, semicircular-shaped plates urged toward their sealing, non-flow position by a pair of helical springs wound about a central pivot rod. Each spring biasses one of the semicircular plates to its sealing position, which biassing force is overcome by the upstream pressure of the fluid impinging upon the upstream sides of the plates, to thus force open the plates by pivoting them against such biassing force. The degree to which the plates pivot about the pivot rod is dependent upon the upstream pressure thereon, with the spring constant of each helical spring determining the pressure at which the check valve opens to allow flow therethrough. These check valves have found use in practically all areas of fluid flow, and have proven to be highly effective, owing to the quick response time thereof, excellent sealing qualities, and lack of wear of its parts because of the initial displacement of the pivoted edge of each plate away from the transverse rib of the valve body constituting a portion of the valve seat. This initial displacement of the hinge-side edge of each plate allows for the seal thereof facing upstream to be first removed from contact with any portion of the valve body, to thus eliminate the need to overcome the added friction caused by the seal's contact with the valve body during the pivotal movement of the plate during opening and closing, which contact previously had caused unequal closing of one plate relative to the other plate, and necessitated greater torque requirements for closing and opening, as well as compromising the reaction time of the valve itself to changes of pressure both upstream and downstream of the pair of plates. An alternative construction is the mounting of the seal itself to the valve body at the inlet thereof, so that when the plates first are moved during opening, their contact against the seal is eliminated during the pivotal opening thereof.
The dual-plate check valve described above also is advantageous in that it has proven to be effective without any attendant disadvantage of head or pressure loss, especially for larger sizes thereof. In addition, since the flow through the valve itself is central, and since the hinge-side of each plate is, initially lifted away from contact with the valve body before pivoting open, flow of the fluid through the valve occurs both on the outside of each plate and on the inside of each plate, thus eliminating eddy currents that in other valves, such as butterfly valves, had caused turbulence and associated pressure and head loss.
The above-described valve has hitherto had use only as a check valve, either allowing flow through a conduit with which it is connected, or preventing such flow. Though the flow rate and upstream and downstream pressure differentials help to determine the precise flow rate of the fluid through the valve, a check valve is mainly designed to allow flow in one direction only, while preventing flow in the opposite direction. For flow systems in which the rate of fluid flow must be controlled, rather than the simple direction of flow, control valves are used instead. A typically-used control valve is a butterfly valve in which a pivotal circular disc is rotated by a control member to allow a flow area through the valve body commensurate with the desired flow rate. However, conventional butterfly valves suffer from the same disadvantages noted above with regard to the flow characteristics of swing check valves, in that large eddy currents form, reducing pressure and increasing head loss, and also require the relatively-large application of controlling torque to operate the pivotal disc in order to overcome the frictional losses associated with these conventional designs. Further, butterfly valve discs are always under circumferential pressure, and a relatively large amount of torque is required to initially unseat or close this disc, because of the frictional losses associated with the seal rubbing against the valve seat.
Applicant has discovered that the dual-plate check valve construction above-described offers enourmous advantages for use as a control valve, which overcomes the disadvantages and deficiencies noted above with regard to conventional butterfly valves, as well as other currently-used control valves, which construction, with some modification, is readily adaptable and usable as a control valve for use in most environments currently serviced by other control valves, such as butterfly valves. With the modification to the structure of the dual-plate check valve according to the present invention, along with the novel control-actuating structure for converting the check valve to a control valve, the present invention provides a control valve that is superior to other conventional and currently-used control valves in: Pressure loss, reduction of eddy currents, torque requirements for operation and control, and frictional losses due to seal-contact against the valve body. Torque requirements for all manipulations of the control member for a desired flow-rate is considerably reduced with the novel control valve of the present invention, as compared with conventional control valves, such as butterfly valves, regardless of the size of valve used.